Polydectes was the king of the island of Seriphos in Greek mythology, son of Magnes and a Naiad; or Peristhenes and Androthoe; or Poseidon and Cerebia.

He was the ruler of the island when Danae and her son Perseus were washed ashore and his brother Dictys saved them. Polydectes fell in love with Danae, but Perseus kept him at a distance, trying to protect his mother. So, Polydectes made a plot to get rid of him; he said that he was going to marry Hippodamia, so everyone should bring in gifts for the wedding. However, Perseus, being poor, did not bring anything, so Polydectes ordered him to bring the head of the GorgonMedusa. Medusa was a fearsome creature, with snakes instead of hair, and she turned into stone anyone who would look into her eyes. Perseus managed to slay Medusa by looking her reflection on his shield, and returned to Seriphos. There, he found out that Danae was mistreated and abused by Polydectes, and that she had sought refuge in a temple. So, Perseus, enraged, entered the court when Polydectes was there, who did not believe that Perseus had actually slain Medusa. As a proof, Perseus took the head out of the bag he was carrying and turned everyone who was present into stone. He then gave the reign of the island to Dictys.